Tuned to Perfection: Ironing Out the Defects in Metal–Organic Framework UiO-66

Metalorganic frameworks (MOFs) are a relatively newclass of crystalline porous materials. One family of these materials that has attracted considerable attention due to their high thermal, chemical, and mechanical stability is the zirconium based MOFs of the UiO family. The material with benzene-1,4-dicarboxylic acid (BDC) as linker is named UiO-66 and is considered to be the parent of the series, from which other members are derived via isoreticular synthesis. A multitude of synthetic procedures has been reported for UiO- 66, with the majority of groups utilizing their own strategies in favor of using one from the pool of pre-existing protocols. With the exception of two recent studies in which the effect of HCl and acetic acid were respectively investigated, there is a lack of understanding of how the product is affected by changes in synthesis parameters. It is especially important to attain such knowledge on UiO MOFs given that past studies have demonstrated there to be several ways in which a given UiO-66 sample may differ from the idealized, non-defective material of composition Zr6O4(OH)4(BDC)6. The most dramatic way that a sample may deviate from ideality is that it may have a significantly lower thermal stability than expected, an issue which has not been previously reported. Figure 1 (discussed in depth later) demonstrates the surprisingly wide variation in the thermal stabilities of three UiO-66 samples synthesized at different temperatures, highlighting how severely the material can be affected by alterations to the synthesis conditions.